Anybody thinking of using a Migration agent ensure they are registered for example if they give UK Immigration advice they should be registered with the OISC in the UK.
In Thailand we have only two companies that are registered with offices in the UK/Thailand,in ASIA anyone can set an office up making false claims etc. Either do the application yourself or use an agent who has demonstrated proven ability with entry clearance applications. You can check their registration here for example mine is F200700163 http://oisc.gov.uk/.